Trivalent Chromium Electroplating Solution and an Operational Method Thereof

ABSTRACT

A trivalent chromium-based electroplating solution in accordance with the present invention a trivalent chromium salt, a bivalent nickel salt, a complex agent, a conductive salt, a buffering agent and an additive for electroplating a chromium-nickel alloy deposit on a component. By using the lowly toxic trivalent chromium to substitute highly toxic hexavalent chromium, an electroplating procedure with the present trivalent chromium-based electroplating solution has less pollution and high current efficiency to allow the electroplating performing at the room temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electroplating technology. It provides a lowly toxic trivalent-chromium based electroplating solution which is used for obtaining a chromium-nickel alloy deposit on a metal component. The electroplating is conducted with high current efficiency at room temperature. An electroplating procedure is also disclosed in this invention. From the proposed electroplating solution, a leveling and brightening chromium-nickel deposit can be easily achieved. Furthermore, chromium-nickel deposits with different ratios of chromium and nickel concentrations could be obtained by varying electroplating current density. Both decorative and hard chromium-based deposits could be achieved from the proposed trivalent chromium-based electroplating solution.

2. Description of Related Art

The chromium-nickel alloys have been widely used in application owing to its superior mechanical properties and corrosion resistance. Conventional electroplating method to obtain the chromium-nickel alloy deposit is performed at a high electroplating temperature (≧50° C.) in a hexavalent chromium-based bath with an addition of nickel sulfate. Owing to highly toxic in nature and RoHS limitation, the hexavalent chromium-based solution is not suitable to be applied for obtaining chromium and chromium alloy deposits. Therefore, to achieve a chromium-nickel alloy deposit in a low-toxic trivalent chromium-based solution has been attracted much more attention in recent years. Up to now, the current efficiency of electrodeposition in a hexavalent chromium-based solution is normally less than 20%. However, the current efficiency in our proposed trivalent chromium-based solution is approximately to be 50%. This has more efficiency for obtaining decorative and hard chromium-based deposits. Moreover, the deposits of chromium-nickel alloys with different ratios of chromium and nickel concentrations can be achieved from the proposed trivalent chromium-divalent nickel electroplating solution by varying plating current densities.

SUMMARY OF THE INVENTION

The main objective of present invention is to provide a trivalent chromium-divalent nickel solution in which a chromium-nickel alloy deposit can be obtained by electroplating at a room temperature with high current efficiency.

To achieve foregoing main objective, the trivalent chromium-based electroplating solution comprises a water solution added with 0.1-1.2 mole/L of a trivalent chromium salt; 0.1-0.8 mole/L of a bivalent nickel salt; 0.1-4.0 mole/L of a complex agent; 1.0-3.0 mole/L of a conductive salt; 0.1-0.8 mole/L of a buffering agent, and 0.01-0.30 mole/L of an additive.

The trivalent chromium-based electroplating solution has low toxicity. The proposed solution can be directly applied to obtain a chromium-nickel alloy deposit on a metallic component by electrodeposition.

Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of an electroplating procedure using a trivalent chromium-based electroplating solution in accordance with the present invention;

FIG. 2 is a SEM (Scanning Electronic Microscopy) micrograph showing the surface morphology of a chromium-nickel deposit achieved with the electroplating procedure in the proposed trivalent chromium-based electroplating solution;

FIG. 3 is an EDS (energy-dispersive x-ray spectrometer) spectrum of the chromium-nickel deposit obtained with the electroplating in the trivalent chromium electroplating solution; and

FIG. 4 is a SEM (scanning electron microscopy) micrograph showing the cross-section view of the chromium-nickel deposit obtained with electroplating in the trivalent chromium-based electroplating solution, wherein the deposit thickness is ca. 10 μm on a copper substrate.

DETAILED DESCRIPTION OF THE INVENTION

A trivalent chromium-based electroplating solution in accordance with the present invention contains a trivalent chromium salt, a bivalent nickel salt, a complex agent, a conductive salt, a buffering agent and an additive for electroplating a chromium-nickel deposit on a metal component. By using the lowly toxic trivalent chromium ion to substitute highly toxic hexavalent chromium ion, the present trivalent chromium-based electroplating solution has much less pollution and high current efficiency to obtain chromium-nickel deposits with different ratios of chromium and nickel concentrations. Moreover, the electroplating can be conducted at room temperature.

The trivalent chromium-based solution comprises: 0.1-1.2 mole/L of the trivalent salt that is selected from the group consisting of chromium chloride, chromium sulfate, or a hydrate of each forgoing salts; 0.1-0.8 mole/L of the bivalent salt that is selected from the group consisting of nickel chloride, nickel sulfate, and a hydrate of each forgoing salts; 0.1-4.0 mole/L of complex agent that is selected from the group consisting of urea (carbamide), glycine (aminoacetic acid), hydroxyacetic acid, formic acid and a dissoluble salt of each forgoing acids; 1.0-3.0 mole/L of the conductive salt that is selected from the group consisting of ammonium chloride, sodium chloride, potassium chloride, magnesium chloride, ammonium sulfate, sodium sulfate, potassium sulfate and magnesium sulfate and a mixture of forgoing salts; 0.1-0.8 mole/L of the buffering agent that is selected from the group consisting of boric acid, aluminum chloride, aluminum sulfate and a mixture of foregoing components; and 0.01-0.30 mole/L of the additive that is selected from the group consisting of ammonium bromide, sodium bromide and potassium bromide and a mixture of foregoing components.

The electroplating procedure is to put a metal component, solid auxiliary electrodes and the trivalent chromium-based electroplating solution into a chemical tank to electroplate a chromium-nickel alloy on the component surface. An additional power supplier is required to provide a stable constant current during electroplating.

Wherein, the temperature of the trivalent chromium-based electroplating solution lies in a range from 1° C. to 50° C., the fixed current density provided by the additional power supplier is in a range from 1 to 90 ampere per square decimeter, and the auxiliary electrodes are made of material selected from the group comprising a titanium mesh coated with platinum, platinum, graphite and stainless steel.

By using the trivalent chromium-based electroplating solution in the present invention in accordance with FIG. 1, the electroplating procedure thereof applied to chromium-nickel alloy electrodeposition comprises steps of: preparing a component, degreasing, washing, activating surface of the component, washing, electroplating by the trivalent chromium-based solution thereof, washing, and drying etc. Each step is further illustrated as following:

-   -   (a) Preparing a component: a component is shaped and prepared.     -   (b) Degreasing: the prepared component is degreased with a         degreasing agent to remove oil and dirt from its surface.     -   (c) Washing: the prepared component is washed to remove the         degreasing agent and to keep the surface clean.     -   (d) Activating component surfaces: the component is dipped into         an acid or alkaline solution to activate surface of the         component by adding an oxidant or by providing electricity so as         to enhance the binding strength between the component surface         and the chromium-nickel alloy deposit.     -   (e) Washing: the surface of the component is cleaned by water.     -   (f) Electroplating the chromium-nickel alloy deposit: this step         is substantially composed of following sub-steps:         -   (f1) Preparing: the component, auxiliary electrodes, and the             trivalent chromium-based electroplating solution are putted             into a tank.         -   (f2) Setting: the component and the auxiliary electrodes             contact the trivalent chromium-based electroplating             solution.         -   (f3) Electroplating: a fixed current or potential is applied             between the component and the auxiliary electrodes by an             additional power supplier to start electroplating.     -   (g) Washing: the surfaces of the component are cleaned by water         after electroplating.     -   (h) Drying: after washing, residual moisture is removed from the         surfaces of the component to make the surfaces to be dried         rapidly.

With further reference to FIG. 1, when electrodeposition of the chromium-nickel alloy deposit is performed, the component surfaces are firstly washed and degreased, activated, and then dipped into the trivalent chromium-based electroplating solution in a chemical tank. Wherein, the trivalent chromium-based electroplating solution is evenly stirred by mechanical methods which would be provided with an additional power supplier. During electrodeposition, the chromium complex and nickel ions could be reduced to form a chromium-nickel alloy deposit on the component surfaces. Thereby, the component surfaces have an even uniform chromium-nickel alloy deposit (as shown in FIGS. 2, 3 and 4).

According to above description, the trivalent chromium-based electroplating solution and the electroplating procedure thereof have the following advantages:

1. The conventional electroplating containing hexavalent chromium ions is highly toxic. By replacing the hexavalent chromium ions with the trivalent chromium ions in the present invention, the electroplating operation is safe to users and waste water meets the standard requirements of environmental protection and industrial safety.

2. The conventional electroplating with a hexavalent chromium-based solution is performed at high temperatures. However, the electroplating solution in the present invention contains trivalent chromium and bivalent nickel enables the electroplating to be conducted at a room temperature and to obtain a decorative or hard chromium-nickel alloy deposit with very good quality.

3. The chemical composition of chromium-nickel alloy deposit is adjusted by different electroplating operation conditions. For example, when the current density is relatively low at 10 A/dm², the chromium-nickel deposit contains 95 wt % of nickel. For another example, when the current density is relatively high at 30 A/dm², the chromium-nickel deposit contains 85 wt % of nickel.

4. By using the lowly toxic trivalent chromium-based solution, electroplating enables to be operated at the room temperature to obtain an leveled and brightened chromium-nickel alloy deposit. Moreover, the current efficiency of electrodeposition is more than 50% so that the electroplating with the proposed solution is energy-saving.

Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed. 

1. A trivalent chromium electroplating solution comprising a water solution added with 0.1-1.2 mole/L of a trivalent chromium salt; 0.1-0.8 mole/L of a bivalent nickel salt; 0.1-4.0 mole/L of a complex agent; 1.0-3.0 mole/L of a conductive salt; 0.1-0.8 mole/L of a buffering agent; and 0.01-0.30 mole/L of an additive.
 2. The trivalent chromium electroplating solution as claimed in claim 1, wherein the trivalent chromium salt selected from the group consisting of chromium chloride, chromium sulfate, or a hydrate of each forgoing salt.
 3. The trivalent chromium electroplating solution as claimed in claim 1, wherein the bivalent nickel salt is selected from the group consisting of nickel chloride, nickel sulfate, or a hydrate of each forgoing salt.
 4. The trivalent chromium electroplating solution as claimed in claim 1, wherein the complex agent is selected from the group consisting of urea (carbamide), glycine (aminoacetic acid), hydroxyacetic acid, formic acid or a dissoluble salt of each forgoing acid.
 5. The trivalent chromium electroplating solution as claimed in claim 1, wherein the conductive salt is selected from the group consisting of ammonium chloride, sodium chloride, potassium chloride, magnesium chloride, ammonium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate or a mixture of forgoing salts.
 6. The trivalent chromium electroplating solution as claimed in claim 1, wherein the buffering agent is selected from the group consisting of boric acid, aluminum chloride, aluminum sulfate or a mixture of foregoing components.
 7. The trivalent chromium electroplating solution as claimed in claim 1, wherein the additive is selected from the group consisting of ammonium bromide, sodium bromide, potassium bromide or a mixture of foregoing components.
 8. An electroplating procedure with a trivalent chromium-based electroplating solution comprising a water solution added with 0.1-1.2 mole/L of a trivalent chromium salt; 0.1-0.8 mole/L of a bivalent nickel salt; 0.1-4.0 mole/L of a complex agent; 1.0-3.0 mole/L of a conductive salt; 0.1-0.8 mole/L of a buffering agent; and 0.01-0.30 mole/L of an additive to deposit a chromium-nickel coating layer, the operational method comprising steps of: arranging a component, auxiliary electrodes, and the trivalent chromium-based electroplating solution in a tank; setting the component and the auxiliary electrodes to contact the trivalent chromium-based electroplating solution; and providing a fixed current or potential between the component and the auxiliary electrodes by an additional power supplier.
 9. The operational method as claimed in claim 8, wherein a temperature of component surfaces lies in a range from 1° C. to 50° C.
 10. The operational method as claimed in claim 8, wherein the fixed current provided by the additional power supplier has a range from 1 to 90 ampere per square decimeter.
 11. The electroplating procedure as claimed in claim 8, wherein the auxiliary electrodes are made of material selected from the group comprising a titanium mesh coated with platinum, platinum, graphite and stainless steel. 